A tilting, or leaning, vehicle has generally three or four wheels, and its body is able to tilt, or lean, into the direction of a turn. This feature allows tilting or leaning vehicles to corner safely and with stability, despite having a narrow track and a high center of gravity. Single track vehicles such as motorcycles and bicycles are not called tilting vehicles, and having only two wheels does not allow their leaning to be controlled by a suspension device (other than gyroscopic systems).
Several configurations for a tilting vehicle are possible such as two front wheels and one rear wheel, one front wheel and two rear wheels, or four wheels. More than four wheels would be possible but not practical.
Generally, the rider is responsible for balancing the vehicle primarily through steering and counter-steering inputs.
To assist the rider in controlling the vehicle, suspension systems (tilt control systems) are employed, and the systems can either be passive or active. Passive systems are limited in that it involves providing a returning momentum that helps the vehicle to recover from a tilt (or lean), and a centering momentum that helps keep the vehicle from falling over when stationary. Active systems are able to control and/or assist the dynamic movement of the vehicle depending on the rider steering inputs. Passive systems currently lack the technology required to account for a wide range of operating conditions, especially when vehicle cargo loading changes. On the other hand, fully active systems suffer from high costs and complexity.